A process according to the described prior art is known from DE-PS 36 41 223. Upon entry into the heat exchanger a gas, as medium, is added to the candy stock to be treated. This gas is homogeneously mixed with the candy stock and finally the mixture is put through the heat exchanger. The volume of the candy stock is enlarged by the addition of the gas, such that an improved heat transfer results from the altered mass ratios. The supplied gas creates turbulences inside the stock and the turbulence is responsible that the stock within the heat exchanger is being continuously mixed such that the heat received by the stock at the heat exchanger wall is immediately carried away. This is done to counteract the danger of the candy stock to be heated at least partially burning and spoiling.
Never-the-less, one observes that especially temperature sensitive candy stock--delicately treated--as, for example, during the manufacturing of milk-caramel stock, will depend upon the milk composition, the milk portion of the total mass and the actual temperature level, result in burning of milk inside the heating coil of the heat exchanger. Such burnings and cakings (build-ups) of materials or portions of materials are mainly found at the beginning of the heating coil within the heat exchanger, while they are barely or not at all found at the end of the heating coil, i.e. the area pointing toward the receiving tank.
On the other hand, it is known that adding some elements inside the heating coil leads to a higher swirl or turbulence formation of the candy stock within the heating coil, which also improves the heat transfer. Here, the disadvantage is that these added elements often create dead spot in which the candy stock remains for prolonged periods of time in an uncontrolled manner and which can lead to burning. Heating coils of that design can only be cleaned with great difficulty and require a great deal of effort, without being able to guarantee success. Apart from that the turbulence formation cannot be changed during operation such that a control of this process is not possible.
DE PS 38 21 505 reveals a process to manufacture hard-candy stock continuously from a watery solution of ingredients whereby the candy stock is also heated in a heating coil of a heat exchanger. A downstream receiving tank space is provided to allow steam to escape, and in which BRUDEN can be removed. The material is then transferred by way of a control valve into a chamber in which, depending upon the degree of vacuum additional steam is removed. Additionally installed devices, downstream, enable the addition of flavors, handling the material as it comes out of the machine and subsequent processing of the candy stock. The vacuum in the vacuum chamber also affects the condition in the steam escape area of the receiving tank all the way into the heating coil of the heat exchanger, such that an enrichment of the dry substance of the candy stock can be accomplished at comparatively low temperature. The problem of burning temperature sensitive candy stocks inside the heating coil is here not discussed.